Buggy code:
public class StrBuilder implements Serializable , Appendable , CharSequence , Builder < String > { static final int CAPACITY = 32 ; private static final long serialVersionUID = 7628716375283629643L ; protected char [ ] buffer ; protected int size ; private String newLine ; private String nullText ; public StrBuilder ( ) { } public StrBuilder ( int initialCapacity ) { } public StrBuilder ( final String str ) { } public String getNewLineText ( ) { } public StrBuilder setNewLineText ( final String newLine ) { } public String getNullText ( ) { } public StrBuilder setNullText ( String nullText ) { <START_BUG> if ( ( nullText != null ) && ( ( nullText . length ( ) ) == 0 ) ) { <END_BUG> nullText = null ; } this . nullText = nullText ; return this ; } @ Override public int length ( ) { } public StrBuilder setLength ( final int length ) { } public int capacity ( ) { } public StrBuilder ensureCapacity ( final int capacity ) { } public StrBuilder minimizeCapacity ( ) { } public int size ( ) { } public boolean isEmpty ( ) { } public StrBuilder clear ( ) { } @ Override public char charAt ( final int index ) { } public StrBuilder setCharAt ( final int index , final char ch ) { } public StrBuilder deleteCharAt ( final int index ) { } public char [ ] toCharArray ( ) { } public char [ ] toCharArray ( final int startIndex , int endIndex ) { } public char [ ] getChars ( char [ ] destination ) { } public void getChars ( final int startIndex , final int endIndex , final char [ ] destination , final int destinationIndex ) { } public StrBuilder appendNewLine ( ) { } public StrBuilder appendNull ( ) { } public StrBuilder append ( final Object obj ) { } @ Override public StrBuilder append ( final CharSequence seq ) { } @ Override public StrBuilder append ( final CharSequence seq , final int startIndex , final int length ) { } public StrBuilder append ( final String str ) { } public StrBuilder append ( final String str , final int startIndex , final int length ) { } public StrBuilder append ( final String format , final Object ... objs ) { } public StrBuilder append ( final StringBuffer str ) { } public StrBuilder append ( final StringBuffer str , final int startIndex , final int length ) { } public StrBuilder append ( final StringBuilder str ) { } public StrBuilder append ( final StringBuilder str , final int startIndex , final int length ) { } public StrBuilder append ( final StrBuilder str ) { } public StrBuilder append ( final StrBuilder str , final int startIndex , final int length ) { } public StrBuilder append ( final char [ ] chars ) { } public StrBuilder append ( final char [ ] chars , final int startIndex , final int length ) { } public StrBuilder append ( final boolean value ) { } @ Override public StrBuilder append ( final char ch ) { } public StrBuilder append ( final int value ) { } public StrBuilder append ( final long value ) { } public StrBuilder append ( final float value ) { } public StrBuilder append ( final double value ) { } public StrBuilder appendln ( final Object obj ) { } public StrBuilder appendln ( final String str ) { } public StrBuilder appendln ( final String str , final int startIndex , final int length ) { } public StrBuilder appendln ( final String format , final Object ... objs ) { } public StrBuilder appendln ( final StringBuffer str ) { } public StrBuilder appendln ( final StringBuilder str ) { } public StrBuilder appendln ( final StringBuilder str , final int startIndex , final int length ) { } public StrBuilder appendln ( final StringBuffer str , final int startIndex , final int length ) { } public StrBuilder appendln ( final StrBuilder str ) { } public StrBuilder appendln ( final StrBuilder str , final int startIndex , final int length ) { } public StrBuilder appendln ( final char [ ] chars ) { } public StrBuilder appendln ( final char [ ] chars , final int startIndex , final int length ) { } public StrBuilder appendln ( final boolean value ) { } public StrBuilder appendln ( final char ch ) { } public StrBuilder appendln ( final int value ) { } public StrBuilder appendln ( final long value ) { } public StrBuilder appendln ( final float value ) { } public StrBuilder appendln ( final double value ) { } public < T > StrBuilder appendAll ( final T ... array ) { } public StrBuilder appendAll ( final Iterable < ? > iterable ) { } public StrBuilder appendAll ( final Iterator < ? > it ) { } public StrBuilder appendWithSeparators ( final Object [ ] array , String separator ) { } public StrBuilder appendWithSeparators ( final Iterable < ? > iterable , String separator ) { } public StrBuilder appendWithSeparators ( final Iterator < ? > it , String separator ) { } public StrBuilder appendSeparator ( final String separator ) { } public StrBuilder appendSeparator ( final String standard , final String defaultIfEmpty ) { } public StrBuilder appendSeparator ( final char separator ) { } public StrBuilder appendSeparator ( final char standard , final char defaultIfEmpty ) { } public StrBuilder appendSeparator ( final String separator , final int loopIndex ) { } public StrBuilder appendSeparator ( final char separator , final int loopIndex ) { } public StrBuilder appendPadding ( final int length , final char padChar ) { }

Fix:
if ( ( nullText != null ) && ( nullText . isEmpty ( ) ) ) {